In IBM i, verifying whether an object exists before performing operations on it is a crucial part of development. This is especially true when dealing with programs that interact with various system objects such as files, data areas, or message files. In this article, I'll walk you through a service program in RPGLE that checks the existence of an object on the system. The service program takes the object name, object type, and an optional object library as parameters.
Publish Time: September 04, 2024
Importance of Checking Object Existence:
1. Prevents Runtime Errors: Trying to access or manipulate an object that doesn't exist can lead to errors in your program, potentially halting execution. Checking for the existence of an object beforehand ensures smooth operations and prevents exceptions.
2. Improves Reliability: When you validate that the object exists, your programs become more reliable. You can implement logic based on whether the object is found, such as creating the object, raising an alert, or skipping specific operations.
3. Saves Resources: By checking object existence before running resource-intensive processes, you can avoid wasting CPU cycles or memory on non-existent objects.
4. Enhances User Experience: In interactive applications, users can be informed about missing objects with meaningful messages instead of encountering system errors.
The RPGLE Service Program:
Here’s a breakdown of a simple RPGLE service program that checks for object existence. The program utilizes IBM i's system APIs, which are highly efficient for system-level tasks like checking object presence.
Parameters:
- Object Name: Name of the object you're checking.
- Object Type: Type of the object (e.g., *FILE, *PGM, etc.).
- Object Library: Optional parameter. If not provided, the default library list will be searched.
How to Use the jsobjexist Service Program
1. Source Code Placement
Ensure the following setup:
- The source code QPROTOSRC/jsobjexist must be placed in the QPROTOSRC source member.
- The source code QRPGLESRC/jsobjexist must be placed in the QRPGLESRC source member.
- Both source members should reside within the same library.
2. Purpose
The QPROTOSRC/jsobjexist member is used within QRPGLESRC to copy the necessary
declarations and parameters for the application to function as a service program. This is achieved by binding
the /copy directive during the compilation process.
Additionally, the QPROTOSRC/jsobjexist source code is utilized by RPG applications that require
this service program.
3. Compilation Instructions
Step 1: Create the Module
CRTRPGMOD MODULE(*CURLIB/jsobjexist) SRCFILE(*CURLIB/QRPGLESRC) SRCMBR(jsobjexist) DBGVIEW(*SOURCE) REPLACE(*YES)
Step 2: Create the Service Program
CRTSRVPGM SRVPGM(*CURLIB/jsobjexist) EXPORT(*ALL) ACTGRP(*CALLER)
Note: The *CURLIB is used as the default library in this example. You may specify any
library where you want the objects to be stored.
4. Binding Directory
Once the service program is created, it should be added to a binding directory. For example, I use JASTOOL as my binding directory. You can use any binding directory that suits your needs.
ADDBNDDIRE BNDDIR(*CURLIB/JASTOOL) OBJ((jsobjexist))
Use Case
To call the Obj_Exists see below example: